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12.7.05

The Dark Side Of The Benefits Of Climate Change

This is a very interesting story, though my thoughts on it are pretty scattered and preliminary:

The Food, the Bad, and the Ugly

A small but growing body of research is finding that elevated levels of atmospheric carbon dioxide, while increasing crop yield, decrease the nutritional value of plants. More than a hundred studies, for example, have found that when CO2 from fossil-fuel burning builds up in plant tissues, nitrogen (essential for making protein) declines. A smaller number of studies hint at another troubling impact: As atmospheric CO2 levels go up, trace elements in plants (such as zinc and iron, which are vital to animal and human life) go down, potentially malnourishing all those that subsist on the plants.

... Scientists have isolated two mechanisms that potentially explain how elevated CO2 levels reduce plant nutrients. The first is a "biomass dilution" effect. As plants absorb more airborne carbon, they produce higher-than-normal levels of carbohydrates but are unable to boost their relative intake of soil nutrients. The result of this dilution effect is increased yields of carbohydrate-rich fruits, vegetables, and grains that contain lower levels of macro- and micronutrients. Put simply, a bite of bread in our current CO2 atmosphere ends up being more nutritious than one in the CO2-enriched atmosphere of the future.

A second problem: Plants exposed to increased CO2 levels start to narrow the stomata through which they inhale CO2 and exhale water vapor via transpiration. This benefits plants by making them more drought resistant, but it also means that fewer waterborne nutrients flow into the roots.


This process seems so obvious once it's explained that I'm surprised I hadn't thought of it -- I suppose I've just been too quick to minimize the yield increases from increased CO2 since that point is most often raised by people who have shown a remarkably poor grasp of other aspects of climate change.

Avoiding increased CO2 is looking more and more like a pipe dream, so the big question is how we can adapt to this problem. The obvious technophilic answer is genetic engineering to address the stomata-narrowing, and fertilizers to address the dilution. Both of these, however, present serious political-economic problems, most notably in increasing the power of multinational agricultural companies. And at present it's the political economy of food and land access, not the volume of food production, that's the major cause of hunger.

Another interesting route is that the increased yields may allow for an undoing of the green revolution. The main effect of the green revolution was to increase the caloric output of crops. This had the benefit of reducing starvation, but brought a number of costs -- farmers are beholden to the companies that supply their seeds and fertilizer, and they wind up monocropping (which is both bad for the ecology of the region and increases vulnerability to disturbances like pests and weather). What I've heard from people doing ethnographic research is that the farmers themselves are similarly ambivalent about the relative merits of the switch.

Increased CO2, however, could increase yields of pre-green-revolution crops so that they were comparable to those of green revolution crops under current CO2 concentrations. Thus they would get an output boost comparable to the current green revolution, while avoiding the overproduction of empty calories that would result from combining green revolution crops and increased CO2. At the same time, the crops would be more adapted to local conditions and more suitable for intercropping, which would reduce vulnerability to disturbances and perhaps even result in more efficient uptake of micronutrients from the local soil.

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